Conventionally, in a process of forming a vertical power device on a silicon carbide semiconductor base body, informing an electrode for connecting a power device with an external electric circuit or the like such as a drain electrode, for example, there has been a demand for the formation of an ohmic electrode on the silicon carbide semiconductor base body for reducing a contact resistance between the silicon carbide semiconductor base body and the drain electrode or the like.
As a first method of forming an ohmic electrode, there has been known a method where an Ni silicide layer is formed on a silicon carbide semiconductor base body by a silicide process where an Ni thin film is formed on a silicon carbide semiconductor base body and, thereafter, heat treatment is performed. However, in the above-mentioned first method, to form the Ni silicide layer by generating a reaction between Ni derived from an Ni thin film and Si derived from a silicon carbide semiconductor base body, heat treatment at a temperature of 1000° C. or above is necessary. Accordingly, when an element is formed on the silicon carbide semiconductor base body in advance, there exists a drawback that the element is broken.
In view of the above, as a method of forming an ohmic electrode, a second method which can overcome the above-mentioned drawback has been known (see patent literature 1, for example). The second method is performed as follows. An element (MOS structure) not shown in the drawing is formed on a first main surface 912 of a silicon carbide semiconductor base body 910 (see FIG. 10A and FIG. 10B). Then, a protective film 916 is formed on the first main surface 912 of the silicon carbide semiconductor base body 910 and, thereafter, unevenness is formed on a second main surface 914 of the silicon carbide semiconductor base body 910 by polishing the second main surface 914 (see FIG. 10C). Then, a thin metal film 918 made of metal capable of forming silicide (for example, an Ni thin film) is formed on the second main surface 914 (see FIG. 10D). Next, a metal silicide layer 920 is formed between the silicon carbide semiconductor base body 910 and the thin metal film 918 by irradiating a laser beam which falls within an ultraviolet region onto the thin metal film 918 thus forming an ohmic electrode 924 (see FIG. 11A). In patent literature 1, after the ohmic electrode 924 is formed, a drain electrode 926 is formed on the ohmic electrode 924 (see FIG. 11B), and a source electrode 928 and a gate electrode not shown in the drawing are formed on a first main surface 912 side of the silicon carbide semiconductor base body 910 (see FIG. 11C) thus manufacturing a power MOSFET.
According to the second method, the metal silicide layer is formed by irradiating a laser beam which falls within an ultraviolet region and hence, unlike the above-mentioned first method, heat treatment at a high temperature becomes unnecessary. Accordingly, even when an element is formed on a silicon carbide semiconductor base body in advance, there is no possibility that the element is broken whereby an ohmic electrode can be formed after the element is formed on the silicon carbide semiconductor base body.